STRUCTURE DETERMINATION OF YEAST COFILIN. A A.

Fedorov*, P. Lappalainen**, E.V. Fedorov*, D.G. Drubin**, S.C. Almo* *Department of Biochemistry, Albert Einstein College of Medicine, Bronx, NY 10461; **Department of Molecular and Cell Biology University of California 94720.

Cofilin is a widely distributed actin-associated protein that binds both F- and G-actin, and severs actin filaments in a pH dependent, calcium independent manner. These activities can be inhibited by phosphoinositides. Two crystal forms of yeast cofilin have been obtained: monoclinic (space group C2, with two molecules in asymmetric unit) and orthorhombic (space group P2₁2₁2₁, one molecule in asymmetric unit). The crystal structure of the orthorhombic form has been determined by multiple isomorphous replacement and anomalous scattering methods and refinement of the structure et 2.3Å resolution is in progress. Cofilin is built around a central five-stranded mixed b-sheet which is sandwiched between a pair of [[alpha]]-helices on each face. A comparison to the actin-severing proteins severin, gelsolin and villin, which display the same overall topology, will be presented. The structure of cofilin provides a basis for understanding its interactions with actin and phosphoinositides.